The disclosure of Japanese Patent Application No. 2000-121571 filed on Apr. 21, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The present invention relates to a technology for controlling an internal combustion engine of a hybrid vehicle having two driving sources comprised of an internal combustion engine and an electric motor.
2. Description of Related Art
In recent years, a hybrid vehicle having two driving sources comprised of an internal combustion engine and an electric motor has been developed in order to reduce fuel consumption in the internal combustion engine, emission gas discharged from the internal combustion engine, noise and the like.
The aforementioned hybrid vehicle includes an internal combustion engine, a power generator driven with part of output from the internal combustion engine, a battery for accumulating electric power generated by the power generator, an electric motor to be driven by electric power from the power generator or battery and a drive power dividing mechanism for distributing the output of the internal combustion engine selectively to the power generator and wheels.
In the hybrid vehicle having such a structure, for example, transmission of the output from the internal combustion engine to the power generator and wheels is interrupted when the vehicle is stopped or at the same time when operation of the internal combustion engine is stopped, a supply of electric power of the battery and power generator to the electric motor is stopped.
In the aforementioned hybrid vehicle, when the vehicle is started or has a low load, transmission of output from the internal combustion engine to the power generator and wheels is interrupted or operation of the internal combustion engine is stopped while electric power of the battery is applied to the electric motor. In this case, the hybrid vehicle is driven with only output of the electric motor driven with electric power from the battery.
In the aforementioned hybrid vehicle, in its normal traveling, the internal combustion engine is started so that an output of the internal combustion engine is transmitted to both the power generator and wheels, and electric power generated by the power generator is applied to the electric motor. In this case, the hybrid vehicle is driven with the output of the internal combustion engine and the output of the electric motor driven with electric power of the power generator.
In the aforementioned hybrid vehicle, when a high load is applied thereon for acceleration or the like, the internal combustion engine is started so that an output of the internal combustion engine is transmitted to both the power generator and wheels and, at the same time, electric power generated by the power generator and electric power from the battery are applied to the electric motor. In this case, the hybrid vehicle is driven with the output of the internal combustion engine and the output of the electric motor driven with electric power from the power generator and battery.
In the aforementioned hybrid vehicle, when the vehicle is decelerated or braked, transmission of the output from the internal combustion engine to the power generator and wheels is interrupted or operation of the internal combustion engine is stopped and rotation force of the wheels is transmitted to the electric motor. In this case, the electric motor functions as a power generator to regenerate power and electric power regenerated by the electric motor is charged to the battery.
In the aforementioned hybrid vehicle, if the amount of accumulated electricity of the battery drops below a predetermined value, the internal combustion engine is started and the output of the internal combustion engine is increased. Then, the output of the internal combustion engine is transmitted to the power generator and all or part of electric power generated by the power generator is charged.
Because the internal combustion engine can be operated effectively in the hybrid vehicle, reduction of fuel consumption rate, reduction of the discharge amount of emission gas, reduction of emission gas and reduction of noise can be achieved.
Further, in the aforementioned hybrid vehicle, if the temperature of the emission gas purifying catalyzer or emission gas purifying part such as air-fuel ratio sensor is less than an activation temperature, the vehicle is started with the electric motor as a main drive source and then, by worsening net heat efficiency of the internal combustion engine, heat amount of emission gas is increased so as to warm up the emission gas purifying part or carry out warm-up operation control.
However, because the aforementioned warm-up operation control takes warm-up of the emission gas purifying part, even if acceleration request for the vehicle is generated during execution of the warm-up operation control, the output of the internal combustion engine cannot be increased. As a result, a desired vehicle driving power cannot be obtained so that drivability may be worsened.
As a technology relating to the invention, Japanese Patent Application Laid-Open No. 11-173175 has disclosed an internal combustion engine control unit for a hybrid vehicle. In the aforementioned internal combustion engine control unit for the hybrid vehicle described in the same publication, a hybrid mechanism for driving the vehicle by selectively using the internal combustion engine and electric motor is provided so as to drive the vehicle with the electric motor as a main drive source when the temperature of the emission gas purifying part is less than its activation temperature and, at the same time, warm up the internal combustion engine. If engine output higher than a maximum output which can be generated by the internal combustion engine being warmed up is requested when the internal combustion engine is warmed up, the operating condition of the internal combustion engine is changed over from the warm-up operation to an operating condition corresponding to the requested engine output.
In the aforementioned internal combustion engine control unit for the hybrid vehicle, the requested engine output is calculated with accelerator opening degree and traveling velocity (or engine rotation number) of the vehicle as parameters.
Thus, when the vehicle is traveling at low speed, even if the accelerator opening degree is large at that time, the requested engine output may sometimes drop below an output which can be generated by the internal combustion engine being warmed up (hereinafter referred to as warm-up time engine output).
Therefore, if the accelerator opening degree is increased quickly with a slow traveling speed like when the vehicle is accelerated from its slow traveling condition, it is estimated that the requested engine output drops below the warm-up time engine output at an initial phase of the acceleration in which the vehicle speed drops and that if the vehicle speed is increased to some extent in the accelerating process, the requested engine output is increased over the warm-up time engine output.
In the aforementioned case, until the requested engine output surpasses the warm-up time engine output, the internal combustion engine is operated in the warm-up condition and after the requested engine output exceeds the warm-up time engine output, the operation of the internal combustion engine is turned to an operating condition fitting to the requested engine output. That is, the operating condition of the internal combustion engine is changed from the warm-up operation condition to the operating condition fitting to the requested engine output during acceleration of the vehicle.
As a result, a change in the output of the internal combustion engine occurs during acceleration of the vehicle, so that a shock may occur due to that output change.
The invention has been achieved in view of the above described problems and provides a technology capable of suppressing an occurrence of a shock due to change-over from a warm-up operation condition to an operation condition fitting to a requested engine output in a hybrid vehicle in which when a necessity of warming up an emission gas purifying part occurs, an electric motor is activated as a main driving source while an internal combustion engine is warmed up, thereby drivability being improved.
An internal combustion engine control unit for hybrid vehicle of one aspect of the invention controls a hybrid mechanism so as to make the electric motor function as a main driving source for the vehicle and warm up the internal combustion engine under a predetermined condition and inhibits the warm-up operation of the internal combustion engine if the requested engine output to the internal combustion engine exceeds a predetermined output or an accelerator opening degree exceeds a predetermined opening degree.
In the internal combustion engine control unit for the hybrid vehicle having such a structure, at the same time when the internal combustion engine is warmed up under a predetermined condition, the electric motor drives the vehicle as a main driving source.
If, when the internal combustion is in the warm-up operation condition, the requested engine output to the internal combustion engine exceeds a predetermined output (for example, a maximum output which can be generated by an internal combustion engine in the warm-up operation condition) or an accelerator opening degree exceeds a predetermined opening degree, the warm-up operation of the internal combustion engine is inhibited. After the inhibition, the operating condition of the internal combustion engine may be changed from the warm-up operation condition to a predetermined operation condition.
That is, according to the control unit of the invention, if the accelerator opening degree exceeds the predetermined opening degree as well as the requested engine output to the internal combustion engine exceeds the predetermined output when the internal combustion engine is in the warm-up operation condition, the operating condition of the internal combustion engine is changed form the warm-up operation condition to the predetermined operation condition. The predetermined operating condition mentioned here refers to an operating condition fitting to the requested engine output.
As a result, if the accelerator opening degree is increased with a slow traveling speed like when the vehicle is accelerated from its slow traveling condition, the operating condition of the internal combustion engine is changed over from the warm-up operation condition to the predetermined operation condition. Thus, the operating condition of the internal combustion engine is not changed during acceleration of the vehicle.
Further, the control unit may estimate a period in which the operating condition should be changed from the warm-up operation condition to the predetermined operation condition and change the operating condition of the internal combustion engine from the warm-up operation condition to the predetermined operation condition gradually prior to the estimated changing period.
In this case, the internal combustion engine in the warm-up operation condition is turned to the predetermined operation condition gradually just before the changing period is reached, so that the output of the internal combustion engine is increased gradually just before the changing period. Therefore, it is possible to make the output of the internal combustion engine agree with the predetermined requested engine output while suppressing a sudden change of the output of the internal combustion engine.
The embodiments of the present invention are not restricted to the above described control unit for the hybrid vehicle. Other embodiments of the present invention are, for example, a hybrid vehicle or hybrid system provided with the aforementioned internal combustion engine control unit and a control method for the internal combustion engine of the same hybrid vehicle.